Thermoplastic, predominantly isotactic homo- and copolymers of 1-butene, referred to herein and in the trade as "polybutylene" or "poly-1-butene," are well known materials. Isotactic polybutylene is the subject of U.S. Pat. No. 3,435,017 of Natta et al. The properties and preparation of isotactic polybutylene are described, for example, in "Encyclopedia of Chemical Technology", edited by Kirk-Othmer, 2nd Ed.,
Suppl. Vol., pp. 773-787. Methods for producing such polybutylene are disclosed, i.a., in U.S. Pat. Nos. 3,362,940 and 3,464,962. Thermoplastic, predominantly isotactic butene-1 homopolymers of the type heretofore described in the literature, e.g., in U.S. Pat. Nos. 3,362,940 and 3,435,017, and produced commercially, are referred to herein as "conventional" polybutylene.
Conventional polybutylene is produced by contact of 1-butene with coordination catalysts which are generally referred to as Ziegler-Natta catalysts. Broadly, such catalysts are the products of contacting a compound of a transition metal of Group IV of the Periodic Table of Elements or of some other transition metals with an organometallic compound of a metal of Groups I-III.
For convenience of reference herein, the transition metal-containing components, which are typically solid, are referred to as "procatalysts", the organometallic compounds as "co-catalysts", and any additional stereoregulating compounds as "selectivity control agents", abbreviated "SCA".
Commercial Ziegler-Natta catalysts are designed to be highly stereoregulating in order to produce highly isotactic polyolefins.
Several generations of Ziegler-Natta coordination catalysts have acquired commercial importance in the production of isotactic polyolefins. Originally, a typical procatalyst was violet TiCl.sub.3 in the delta or gamma crystal form, or a violet TiCl.sub.3 complex, such as with AlCl.sub.3. Several types of more active TiCl.sub.3 procatalysts have since been developed and put to commercial use. The co-catalysts employed with TiCl.sub.3 catalysts are aluminum alkyl compounds, typically halogen-containing aluminum alkyls such as aluminum diethyl halides.
During the last 10 years, more highly active catalysts systems have been developed, particularly for production of isotactic polypropylene. These typically comprise a support of magnesium chloride, which may have been activated such as by ball milling, combined with TiCl.sub.4 and an electron donor--typically an aromatic ester such as ethyl benzoate. The co-catlayst is again an aluminum alkyl, typically an aluminum trialkyl. Generally an electron donor is employed as selectivity control agent. The cocatalyst may be complexed with the selectivity control agent in whole or in part, prior to being combined with the procatalyst. The purpose of the selectivity control agents is to increase the stereoregulating activity of the catalysts. Typical selectivity control agents are aromatic esters such as p-ethyl anisate. Numerous variants of these systems have been disclosed in the patent literature. These catalyst systems, referred to herein as supported coordination catalysts systems, are known to be substantially more active in the production of polypropylene than the most active TiCl.sub.3 -based catalyst systems of the prior art.
The goal of commercial Ziegler-Natta catalysis of propylene or higher alpha-monoolefins generally is the production of highly isotactic polymers. Isotacticity refers to the molecular structure of olefin polymer molecules. The isotactic structure in polyolefins is one in which all the assymetric carbon atoms have the same steric configuration. The isotactic structure of polybutylene is illustrated and discussed in U.S. Pat. No. 3,435,017 to Natta et al. High isotacticity of conventional polymers of butene-1 or of propylene is associated with high crystallinity of the polymers.
The crystallinity of conventional butene-1-homopolymers, determined by X-ray diffraction analysis, is typically in the range from 50 to 55%. Their isotacticity, determined by ether extraction, is typically in the range from 97.5% to 99.5%.
Another highly stereoregular form of polyolefins is known as "syndiotactic". In the syndiotactic structure, alternate assymetric carbon atoms have opposite steric configuration. Syndiotactic polybutylene is described by Natta et al. in Atti Acad. Naz. Lincei, Cl. Sci. Fis, Mat. Nat., Rend. [8 28, 4523 (1960)]. The polymer is an amorphous solid. It was prepared by hydrogenation of syndiotactic polybutadiene. Syndiotactic polyolefins are difficult to produce and are not at present of commercial interest.
Due to its crystallinity, conventional polybutylene exhibits significant stiffness, tensile strength, hardness, and other physical properties characteristics of such polymers as high density polyethylene and isotactic polypropylene. It also shares such other properties of these polyolefins as chemical inertness and dielectric properties.
Outstanding properties of conventional isotactic polybutylene are toughness, resistance to creep and resistance to environmental stress cracking. The exceptional resistance of polybutylene to environmental stress cracking, coupled with the good creep resistance, recommends the use of conventional polybutylene for pipe. The exceptional toughness makes it desirable for the production of film for packaging, since films of conventional polybutylene are significantly stronger than films of other common polyolefins of the same thickness.
Elastomeric polybutylene recovered as a small fraction of a product made with poorly stereoregulating catalysts is known from U.S. Pat. No. 3,435,017 to Natta et al. Another elastomeric polybutylene, having an isotacticity of no more than 50% and produced with a catalyst having poor stereoregulating activity is the subject of U.S. Pat. No. 4,298,722 to Collette et al.
References
"Encyclopedia of Chemical Technology, "Kirk-Othmer, 2nd Ed., Suppl. Vol., pp 773-797 provides a detailed description of the state of the art of polybutylene production in 1967; the commercial aspects have not significantly changed to date.
U.S. Pat. No. 3,435,017 to Natta et al. describes conventional isotactic polybutene-1 and its preparation and properties.
U.S. Pat. No. 3,175,999 to Natta et al. describes polymers of alpha olefins, primarily of propylene, which are designated "stereoisomer" block polymers. They are described as polymers in which isotactic sections alternate with non-isotactic (atactic) sections. Stereoblock polymers are said to be present in small concentrations in conventionally prepared Ziegler-Natta polymers; they must be recovered by a series of solvent extractions, as by treating some of the intermediate fractions of a sequential solvent extraction of Ziegler-Natta polymers with a solvent which has a dissolving capacity for the polyolefin intermediate between that of diethyl ether and n-heptane. In the illustrative examples, the catalysts are compositions which are now known to have poor or very poor stereoregulating ability. In Example 4 of the patent, a polymer of butene-1, produced with a catalyst prepared from vanadium tetrachloride and triethylaluminum, was extracted with hot ether and the residue of the ether extraction was then extracted with methylene chloride to obtain an extract, corresponding to 6% of the residue of the first extraction, which was said to have high reversible elasticity.
U.S. Pat. No. 4,298,722 to Collette et al. is directed to production of an elastomeric polybutene-1 which is made with a poorly stereoregulating catalyst and has an ether solubles content of at least 30% and isotacticity not exceeding 50%. The reaction products illustrated by example, listed in Table 3 of the patent, had ether solubles contents of 38-56% (determined before milling) and isotacticities of 23-46%.
While a large number of patents and patent applications have now been published directed to the production of supported coordination catalyst systems for the stereoregular polymerization of alpha olefins, the only one which have been noted as being specifically directed to the polymerization of butene-1 are the following three patent publications.
European Published Application No. 2522, published June 27, 1979, of Phillips Petroleum Company, is directed to the polymerization of butene-1 to form a polybutylene having the properties of conventional isotactic polybutylene. In order to accomplish this, the patent describes a modified catalyst preparation and a particular slurry polymerization process.
Japanese Kokai Patent No. 54/85293, published July 6, 1979, applied for in Japan on Dec. 21, 1977 by Mitsui Petrochemical Industries Company, is directed to the production of certain copolymers of butene-1 with another alpha monoolefin, having more than 60 but no more than 98% weight butene-1 content and preferably 70-90% butene-1 content and 30-10% propylene. These copolymers are said to have physical characteristics comparable to polyvinyl chloride.
Japanese Patent Application No. 51/23607 published Sept. 24, 1980, applied for in Japan by Mitsui Petrochemical Industries Company, is directed to a modification in the polymerization process for producing conventional polybutylene over catalysts employing as procatalysts a composite of titanium, magnesium, halogen and electron donor.